1. Field of the Invention
The present invention relates to a wind turbine blade, in particular to a partial pitch wind turbine blade.
2. Description of Related Art
A wind turbine blade generally comprises an airfoil shaped profile having a relatively rounded leading edge and a relatively narrow trailing edge, the blade having a suction side (exposed to relatively low air pressure) and a pressure side (exposed to relatively high air pressure).
US patent application No. 2009/0148285 by Scholte-Wassink assigned to GE Energy discloses a wind turbine with a multi-section blade, where the outer section can be pitched relatively to the inner section. A pitch control assemble for an airplane wing is disclosed in U.S. Pat. No. 5,263,846.
FIG. 1 shows an enlarged pitch junction section of a partial pitch wind turbine blade. A partial pitch wind turbine blade 100 comprises an inner blade section 102 and an outer blade section 104 coupled together at a pitch junction, via a pitch system 106. The outer blade section 104 is operable to be pitched relative to the inner blade section 102 by rotation of the pitch system 106. The pitch angle of the outer blade section 104 can be controlled to regulate the operation of the wind turbine, by pitching the outer blade section 104 into or out of the wind direction at the turbine.
With reference to FIG. 2, one feature of partial pitch blades which contributes to efficiency losses in blade performance is the creation of a gap between the trailing edges of the adjacent blade sections, when projected along the longitudinal axis of the blade. In FIG. 2, the inner and outer blade section 102,104 have common leading edge 108, and respective trailing edges 110a,110b, with the pressure side of the overall blade 100 indicated at 112 and the suction side of the overall blade 100 indicated at 114. When the outer blade section 104 is pitched relative to the inner blade section 102, a gap (indicated at 116) is formed in the general blade profile between the two trailing edges 110a, 110b, when seen along the length of the blade 100.
The presence of this trailing edge gap 116 results in air leakage from the pressure side 112 of the blade 100 to the suction side 114, as gap 116 means that there is no barrier between the pressure side of the outer blade section 104 and the suction side of the adjacent inner blade section 102.
Sealing of a gap between adjacent parts of a wing of an airplane has been disclosed in U.S. Pat. No. 5,518,210 by Friberg assigned to McDonnel Douglas Corp. D1 describes a wing where seal plates and attached to the airfoil so that the stream-wise gaps created by the deflected aileron are covered. Prevents airflow leakage through gaps between surface and aerofoil to reduce aerodynamic drag and improve flight efficiency.